What is the difference between - Windows Defender and Microsoft Security Essentials?

A comparison of the difference between the two from Microsoft:

Q: How is this different from Windows Defender?

A: Windows Defender detects and removes known spyware only. It is not designed to protect against the full breadth of malicious software, and specifically does not prevent viruses, worms, Trojans, and other malicious software from infecting your machine. The new no-cost solution will be a comprehensive anti-malware solution.

Q: Is Microsoft Security Essentials designed to replace Windows Defender?

A: No but if you are running Microsoft Security Essentials, you do not need to run Windows Defender. Microsoft Security Essentials is designed to disable Windows Defender in order to manage the PC’s real-time protection, including anti-virus, rootkits, Trojans and spyware.

Microsoft Security Essentials is antimalware software, which means that it's designed to detect and help protect your computer against a wide range of malicious software, including viruses, spyware, and other potentially unwanted software.

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Windows Defender, which is automatically installed with your Windows operating system, is software that detects and stops spyware. To learn more about Windows Defender, visit the Windows Defender Web site.

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